Fix teardown of stale AudioStreamMonitor poll callbacks.

content/browser/media/audio_stream_monitor.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
 #define CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_
 
 #include <map>
 #include <utility>
 
@@ skipping 36 matching lines @@
   // usually called whenever the tab data model is refreshed; but there are
   // other use cases as well (e.g., the OOM killer uses this to de-prioritize
   // the killing of tabs making sounds).
   bool WasRecentlyAudible() const;
 
   // Returns true if the audio is currently audible from the given WebContents.
   // The difference from WasRecentlyAudible() is that this method will return
   // false as soon as the WebContents stop producing sound.
   bool IsCurrentlyAudible() const;
 
+  // Called by the WebContentsImpl if |render_process_id| dies; used to clear
+  // any outstanding poll callbacks.
+  void RenderProcessGone(int render_process_id);
+
   // Starts or stops audio level monitoring respectively for the stream owned by
   // the specified renderer.  Safe to call from any thread.
   //
   // The callback returns the current power level (in dBFS units) and the clip
   // status (true if any part of the audio signal has clipped since the last
   // callback run).  |stream_id| must be unique within a |render_process_id|.
   typedef base::Callback<std::pair<float, bool>()> ReadPowerAndClipCallback;
   static void StartMonitoringStream(
       int render_process_id,
       int render_frame_id,
@@ skipping 99 matching lines @@
   // Number of active streams to be used as a proxy for audibility when power
   // level monitoring is not available.
   size_t active_streams_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioStreamMonitor);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_MEDIA_AUDIO_STREAM_MONITOR_H_